In 3GPP (Third Generation Partnership Project), in a radio communication system corresponding to LTE (Long term Evolution), for which the standards are being set up currently, a radio base station eNB assigns a radio resource in the radio communication between the radio base station eNB and a radio terminal UE (for example, see Non Patent Literature 1). Furthermore, in a radio communication system corresponding to LTE, either one of Frequency Division Duplex (FDD) or Time Division Duplex (TDD) is employed in the radio communication between the radio base station eNB and the radio terminal UE.
Moreover, in an LTE (TDD-LTE) radio communication system employing the TDD, there has been discussed a feature where a radio base station eNB performs control for adaptively directing a beam (adaptive array control) toward the radio terminal UE at the time of transmission of a downlink radio signal, in order to ensure communication quality between the radio base station eNB and a radio terminal UE that is moving.
According to a technique of calculating the antenna weight, when a radio base station eNB receives a sounding reference signal (SRS), which is an uplink radio signal from a radio terminal UE, it is considered that the radio base station eNB calculates an antenna weight for a downlink resource block that has a frequency band equal to a frequency band of the SRS.
In such a case, if the downlink resource block assigned to the radio terminal UE switches frequently, the transmission frequency band of the SRS also needs to be switched in accordance with the switching of the downlink resource block so that the above antenna weight is calculated appropriately. Therefore, a control message for the transmission frequency band of the SRS is transmitted frequently from the radio base station eNB to the radio terminal UE because of which the utilization efficiency of the radio resource declines. Moreover, when the radio base station eNB efficiently assigns a radio resource to a plurality of radio terminals UE, it becomes necessary to be able to perform control in an easy manner.
In view of the above problem, a first object of the present invention is to provide a radio base station and a communication control method, by which the utilization efficiency of a radio resource is improved. Furthermore, a second object of the present invention is to provide a radio base station and a communication control method by which it is possible to assign a radio resource in an easy manner while improving the utilization efficiency of the radio resource.